Adoptive immunotherapy, which involves the transfer of autologous antigen-specific T cells generated ex vivo, is a promising strategy to treat viral infections and cancer. The T cells used for adoptive immunotherapy can be generated either by expansion of antigen-specific T cells or redirection of T cells through genetic engineering (Park, Rosenberg et al. 2011). Transfer of viral antigen specific T cells is a well-established procedure used for the treatment of transplant associated viral infections and rare viral-related malignancies. Similarly, isolation and transfer of tumor specific T cells has been shown to be successful in treating melanoma.
Novel specificities in T cells have been successfully generated through the genetic transfer of transgenic T cell receptors or chimeric antigen receptors (CARs) (Jena, Dotti et al. 2010). CARs are synthetic receptors consisting of a targeting moiety that is associated with one or more signaling domains in a single fusion molecule. In general, the binding moiety of a CAR consists of an antigen-binding domain of a single-chain antibody (scFv), comprising the light and variable fragments of a monoclonal antibody joined by a flexible linker. Binding moieties based on receptor or ligand domains have also been used successfully. The signaling domains for first generation CARs are derived from the cytoplasmic region of the CD3zeta or the Fc receptor gamma chains. First generation CARs have been shown to successfully redirect T cell cytotoxicity, however, they failed to provide prolonged expansion and anti-tumor activity in vivo. Signaling domains from co-stimulatory molecules including CD28, OX-40 (CD134), and 4-1BB (CD137) have been added alone (second generation) or in combination (third generation) to enhance survival and increase proliferation of CAR modified T cells. CARs have successfully allowed T cells to be redirected against antigens expressed at the surface of tumor cells from various malignancies including lymphomas and solid tumors (Jena, Dotti et al. 2010).
Meanwhile, induction treatments for acute myeloid leukemia (AML) have remained largely unchanged for nearly 50 years and AML remains a disease of poor prognosis. Acute myeloid leukemia (AML) is a disease characterized by the rapid proliferation of immature myeloid cells in the bone marrow resulting in dysfunctional hematopoiesis. Although standard induction chemotherapy can induce complete remissions, many patients eventually relapse and succumb to the disease, calling for the development of novel therapeutics for AML.
Recent advances in the immunophenotyping of AML cells have revealed several AML associated cell surface antigens that may act as targets for future therapies. The interleukin 3 receptor alpha chain (IL-3Rα; CD123—NCBI reference: NP_001254642) has been identified as a potential immunotherapeutic target since it is over-expressed on AML tumor cells compared to normal hematopoietic stem cells. Additionally, two phase I trials for CD123-specific therapeutics have been completed with both drugs displaying good safety profiles (ClinicalTrials.gov ID: NCT00401739 and NCT00397579). Unfortunately, these CD123 targeting drugs had limited efficacy suggesting that alternative, and more potent and specific therapies targeting CD123 are required to observe anti-leukemic activity.
A possibly more potent alternative therapy for the treatment of Leukemia could be the use of T cells expressing chimeric antigen receptors (CARs) that redirect T cell specificity towards cell surface tumor associated antigens (TAAs) in an MHC-independent manner. Several groups have developed CARs targeting various antigens for the treatment of B-cell malignancies. However, CAR engineered T cells for the treatment of AML remain scarce.
In particular, there is still a need to improve construction of CARs that show better compatibility with T-cell proliferation, in order to allow the cells expressing such CARs to reach significant clinical advantage.
In addition, there is a need to improve CD123 CARs having the capacity to proliferate and target selectively CD123 expressing cells.
Further, the use of such CAR expressing immune T cell targeting CD123 in combination with cytotoxic chemotherapy agents as a treatment usually employed as anti-cancer treatments remains a problem.
Several cytotoxic agents such as anti-metabolites, alkylating agents, anthracyclines, DNA methyltransferase inhibitors, platinum compounds and spindle poisons have been developed to kill cancer cells, in particular cancer cells expressing CD123.
These chemotherapy agents can be detrimental to the establishment of robust anti-tumor immunocompetent cells due to their non-specific toxicity. Small molecule-based therapies targeting cell proliferation pathways may also hamper the establishment of anti-tumor immunity.
Thus, there is also a need of developing T cells targeting CD123 that would be specific and compatible with the use of drugs, in particular of anti-cancer chemotherapies, such as those affecting cell proliferation.
Thus, to use “off-the-shelf” allogeneic therapeutic cells in conjunction with chemotherapy, the inventors develop a method of engineering allogeneic T-cell, less allogenic and resistant to chemotherapeutic agents. The therapeutic benefits afforded by this strategy should be enhanced by the synergistic effects between chemotherapy and immunotherapy. Moreover, drug resistance can also benefit from the ability to selectively expand the engineered T-cell thereby avoiding the problems due to inefficient gene transfer to these cells.